A standard hammer drill has a drive spindle that is rotated about a spindle axis and a hammer displaceable axially in the drive spindle. A chuck is carried on the spindle so as to rotate therewith, and holds a drill bit having a shaft having a radially outwardly open and at least generally axially extending groove. he chuck holds the drill bit so it is centered on the spindle axis, and the hammer is effective on the rear end of the drill bit. The bit is rotationally coupled to the chuck body, which as mentioned above is rotated, and is at least limitedly axially reciprocated by the hammer so that it can drill through masonry or the like.
The jaws are normally urged radially outward by springs and are displaced radially inward by an adjustment ring which has threads that mate with teeth on the jaws. This ring is formed of a pair of semicircular parts secured together by a knurled sleeve.
Such a construction is relatively complex to manufacture, and to take apart for subsequent service. It has a large amount of parts that are failure prone, in particular the springs which often rust out. Such chucks are also normally axially fairly long, increasing the lever arm applied to the drill spindle and to its bearings.
It is also possible for the chuck to have a tubular chuck body centered on a chuck axis and having a central axially extending bit-receiving passage and a radially outwardly open chuck-key centering hole. A plurality of jaws radially but not angularly displaceable in the chuck body have inner ends engageable with the drill-bit shank in the passage. An adjustment ring connected to the jaws moves same radially synchronously and thereby centers the bit in the body by engagement of the inner ends with the shank. This ring is formed with axially backwardly directed teeth positioned axially forward of the centering hole such that when a chuck key is fitted into the centering hole its crown gear meshes with the ring teeth. A locking sleeve angularly nondisplaceable on the body carries at least one tooth axially engageable between the ring teeth. This sleeve is axially displaceable on the body between an axially forward locking position with the sleeve tooth engaged with the ring teeth and the sleeve positioned relative to the hole such that the key cannot be fitted to the chuck with the gear meshing with the ring teeth and an axially backward freeing position with the sleeve tooth out of engagement with the ring teeth and the sleeve positioned relative to the hole such that the key can be fitted to the chuck with the gear meshing with the ring teeth. A biasing spring is braced between the sleeve and the body for urging the sleeve axially forward into the locking position. Normally the angular-coupling formations are on the jaws.
Such an arrangement is quite complex and not suitable for use in a highly compact or inexpensive hammer drill.